U.S. patent application number 11/480564 was filed with the patent office on 2007-01-25 for variable lift valve operating system for internal combustion engine.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to Takahumi Mizorogi, Hiroyuki Murase, Hidetaka Ozawa.
Application Number | 20070017462 11/480564 |
Document ID | / |
Family ID | 37110224 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070017462 |
Kind Code |
A1 |
Murase; Hiroyuki ; et
al. |
January 25, 2007 |
Variable lift valve operating system for internal combustion
engine
Abstract
In a variable lift valve operating system for an internal
combustion engine, an actuator for rotatably driving a control
shaft of a variable lift mechanism is mounted on an engine body.
The actuator includes an electric motor, a deceleration mechanism,
a transmission mechanism interposed between the control shaft and
the deceleration mechanism, and a default mechanism. A deceleration
mechanism accommodation part for accommodating the deceleration
mechanism and a default mechanism accommodation part for
accommodating the default mechanism are formed in a casing of the
actuator so as to sandwich therebetween a thermally vulnerable part
which is directly connected to the control shaft. Therefore, it is
possible to enhance the degree of freedom of amounting position of
the actuator while heat damage is prevented from generating in the
thermally vulnerable part of the actuator.
Inventors: |
Murase; Hiroyuki; (Wako-shi,
JP) ; Mizorogi; Takahumi; (Wako-shi, JP) ;
Ozawa; Hidetaka; (Wako-shi, JP) |
Correspondence
Address: |
ARMSTRONG, KRATZ, QUINTOS, HANSON & BROOKS, LLP
1725 K STREET, NW
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
HONDA MOTOR CO., LTD.
Tokyo
JP
|
Family ID: |
37110224 |
Appl. No.: |
11/480564 |
Filed: |
July 5, 2006 |
Current U.S.
Class: |
123/90.15 |
Current CPC
Class: |
F01L 13/00 20130101;
F01L 13/0026 20130101 |
Class at
Publication: |
123/090.15 |
International
Class: |
F01L 1/34 20070101
F01L001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2005 |
JP |
2005-200729 |
Jul 8, 2005 |
JP |
2005-200731 |
Jul 8, 2005 |
JP |
2005-200732 |
May 26, 2006 |
JP |
2006-146170 |
Claims
1. A variable lift valve operating system for an internal
combustion engine comprising: an engine valve; a variable lift
mechanism capable of changing a lift amount of the engine valve;
and an actuator which is mounted on an engine body to rotatably
drive a control shaft of the variable lift mechanism and which
includes: an electric motor; a deceleration mechanism which
decelerates output of the electric motor; a transmission mechanism
interposed between the control shaft and the deceleration
mechanism; and a default mechanism capable of rotatably biasing the
control shaft to a position where a lift amount of the engine valve
becomes a predetermined lift amount when the electric motor is not
energized, wherein a deceleration mechanism accommodation part for
accommodating the deceleration mechanism and a default mechanism
accommodation part for accommodating the default mechanism are
formed in a casing of the actuator so as to sandwich therebetween a
thermally vulnerable part which is directly connected to the
control shaft.
2. The variable lift valve operating system for an internal
combustion engine according to claim 1, wherein the thermally
vulnerable part is a sensor which detects a rotation amount of the
control shaft.
3. The variable lift valve operating system for an internal
combustion engine according to claim 1, wherein the thermally
vulnerable part is a synthetic resin worm wheel which constitutes a
part of the transmission mechanism and is fixed to the control
shaft.
4. The variable lift valve operating system for an internal
combustion engine according to claim 1, wherein the default
mechanism further includes a default shaft which is a separate
member from a drive shaft that is moved with and connected to the
control shaft and has an axis parallel with the drive shaft, a
rotary member which is capable of rotating around the axis of the
default shaft and is moved with and connected to the drive shaft,
and a default spring which rotatably biases the rotary member; and
at least a main part of the default mechanism is provided in the
actuator.
5. The variable lift valve operating system for an internal
combustion engine according to claim 4, wherein the default spring
is of a spiral type.
6. The variable lift valve operating system for an internal
combustion engine according to claim 5, wherein the default
mechanism accommodation part is formed in the casing of the
actuator, the default mechanism accommodation part accommodating a
main part of the default mechanism, the main part including at
least the default spring; and a grease is charged into the default
mechanism accommodation part.
7. The variable lift valve operating system for an internal
combustion engine according to claim 1, wherein, in the casing of
the actuator, a plurality of mounting bosses are projectingly
provided at a plurality of spots around the electric motor, bolts
passing through the mounting bosses to fasten the casing to the
engine body; and a plurality of ribs extending to the mounting
bosses are projectingly provided in the casing of the actuator.
8. The variable lift valve operating system for an internal
combustion engine according to claim 1, wherein a deceleration
ratio of the deceleration mechanism is set at a value at which
maximum efficiency of the electric motor is obtained when quickest
response is performed to required driving torque.
Description
RELATED APPLICATION DATA
[0001] The Japanese priority application Nos. 2005-200729,
2005-200731, 2005-200732 and 2006-146170 upon which the present
application is based are hereby incorporated in their entirety
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a variable lift valve
operating system for an internal combustion engine comprising: an
engine valve; a variable lift mechanism capable of changing a lift
amount of the engine valve; and an actuator which is mounted on an
engine body to rotatably drive a control shaft of the variable lift
mechanism and which includes: an electric motor; a deceleration
mechanism which decelerates output of the electric motor; a
transmission mechanism interposed between the control shaft and the
deceleration mechanism; and a default mechanism capable of
rotatably biasing the control shaft to a position where a lift
amount of the engine valve becomes a predetermined lift amount when
the electric motor is not energized.
[0004] 2. Description of the Related Art
[0005] Japanese Patent Application Laid-open No. 2005-42642
discloses an engine valve system, in which an actuator mounted on
an engine body so as to drive a control shaft includes an electric
motor, a screw shaft rotatably driven by the electric motor, and a
nut that is connected to one end portion of a lever whose other end
portion is fixed to the control shaft and that is threadedly fitted
onto the screw shaft.
[0006] It is desirable that some of the components of the actuator
of such a variable lift operating system be made of a synthetic
resin for reduction in weight and friction, and that sensors whose
characteristics change in accordance with the ambient temperature
be mounted to the actuator, but the synthetic resin components and
the sensors are vulnerable to heat. Meanwhile, since the actuator
is mounted on the engine body, the actuator is exposed to
rearward-blowing wind of a radiator or radiation heat from an
exhaust system of the internal combustion engine depending on the
mounting position of the actuator to the engine main body, so that
the degree of freedom of the mounting position of the actuator
using the thermally vulnerable parts is lowered.
SUMMARY OF THE INVENTION
[0007] The present invention has been achieved with the above
circumstances in view, and has an object to provide a variable lift
valve operating system for an internal combustion engine in which
the degree of freedom of a mounting position of an actuator is
enhance while heat damage is prevented from generating in a
thermally vulnerable part of the actuator.
[0008] In order to achieve the above object, according to a first
feature of the present invention, there is provided a variable lift
valve operating system for an internal combustion engine
comprising: an engine valve; a variable lift mechanism capable of
changing a lift amount of the engine valve; and an actuator which
is mounted on an engine body to rotatably drive a control shaft of
the variable lift mechanism and which includes: an electric motor;
a deceleration mechanism which decelerates output of the electric
motor; a transmission mechanism interposed between the control
shaft and the deceleration mechanism; and a default mechanism
capable of rotatably biasing the control shaft to a position where
a lift amount of the engine valve becomes a predetermined lift
amount when the electric motor is not energized, wherein a
deceleration mechanism accommodation part for accommodating the
deceleration mechanism and a default mechanism accommodation part
for accommodating the default mechanism are formed in a casing of
the actuator so as to sandwich therebetween a thermally vulnerable
part which is directly connected to the control shaft.
[0009] With this arrangement of the first feature, the thermally
vulnerable part is sandwiched between the deceleration mechanism
accommodation part and the default mechanism accommodation part
which are formed in the casing. Therefore, the deceleration
mechanism accommodation part and the default mechanism
accommodation part perform the heat shield function for the
thermally vulnerable part, heat damage is prevented from spreading
to the thermally vulnerable part to enhance durability of the
thermally vulnerable part, and heat damage is prevented from
generating in the vulnerable part to enhance the degree of freedom
of a mounting position of the actuator.
[0010] According to a second feature of the present invention, in
addition to the first feature, the thermally vulnerable part is a
sensor which detects a rotation amount of the control shaft. With
this arrangement, although the sensor changes in characteristics in
accordance with the ambient temperature, detection accuracy of the
sensor can be enhanced by preventing the sensor from being directly
exposed to hot air and radiation heat by sandwiching the sensor
between the deceleration mechanism accommodation part and the
default mechanism accommodation part.
[0011] According to a third feature of the present invention, in
addition to the first feature, the thermally vulnerable part is a
synthetic resin worm wheel which constitutes a part of the
transmission mechanism and is fixed to the control shaft. With this
arrangement, it is possible to achieve reduction in weight of the
actuator and reduction in friction by using the worm wheel formed
from a synthetic resin, and prevent heat damage from spreading to
the worm wheel by sandwiching the worm wheel between the
deceleration mechanism accommodation part and the default mechanism
accommodation part, thereby enhancing reliability and durability,
and further preventing increase in friction by thermal deformation
or the like to achieve energy saving.
[0012] According to a fourth feature of the present invention, in
addition to the first feature, the default mechanism further
includes a default shaft which is a separate member from the drive
shaft and has an axis parallel with the drive shaft, a rotary
member which is capable of rotating around the axis of the default
shaft and is moved with and connected to the drive shaft, and a
default spring which rotatably biases the rotary member; and at
least a main part of the default mechanism is provided in the
actuator.
[0013] With this arrangement of the fourth feature, the rotary
member which is a separate member from the drive shaft and rotates
around the axis of the default shaft parallel with the drive shaft
can be moved with and connected to the drive shaft so that the
rotary member rotates in a rotation range of less than one rotation
corresponding to the rotation of the electric motor within the
range of the lift amount change of the engine valve. Therefore, a
conventionally-used default mechanism with high durability and
reliability can be adopted.
[0014] According to a fifth feature of the present invention, in
addition to the fourth feature, the default spring is of a spiral
type. With this arrangement, the default mechanism can be made
compact in the direction along the axis of the default shaft.
[0015] According to a sixth feature of the present invention, in
addition to the fifth feature, the default mechanism accommodation
part is formed in the casing of the actuator, the default mechanism
accommodation part accommodating a main part of the default
mechanism, the main part including at least the default spring; and
a grease is charged into the default mechanism accommodation part.
With this arrangement, sliding friction force which tends to be
large due to the spiral-type default spring is reduced, and the
power which should be exhibited by the electric motor is reduced to
achieve energy saving, leading to reduced fuel consumption.
[0016] According to a seventh feature of the present invention, in
addition to the first feature, in the casing of the actuator, a
plurality of mounting bosses are projectingly provided at a
plurality of spots around the electric motor, bolts passing through
the mounting bosses to fasten the casing to the engine body; and a
plurality of ribs extending to the mounting bosses are projectingly
provided in the casing of the actuator.
[0017] With this arrangement of the seventh feature, the mounting
bosses for mounting the casing to the engine body are provided in
the casing at a plurality of spots in the periphery of the electric
motor, the casing can be firmly fixed to the engine body at the
portion corresponding to the electric motor which is the vibration
generating source of the actuator, thereby enhancing vibration
resistance and durability of the actuator mounted to the engine
body, and enhancing the control accuracy of the control shaft and
controllability of exhaust property. In addition, distortion of the
casing can be prevented by the ribs extending to the respective
mounting bosses, increase in the sliding friction force is avoided
between components, which are supported by the casing and in
contact with each other, among a plurality of components
constructing the actuator, and driving force which should be
exhibited by the electric motor is reduced to achieve energy
saving.
[0018] According to an eighth feature of the present invention, in
addition to the first feature, a deceleration ratio of the
deceleration mechanism is set at a value at which maximum
efficiency of the electric motor is obtained when quickest response
is performed to required driving torque.
[0019] With this arrangement of the eighth feature, the heat
generation amount of the electric motor is minimized when the
variable lift mechanism is under the harshest operational
conditions, extension of the life of the electric motor is achieved
by suppressing heat generation of the electric motor, thermal
distortion is prevented from generating in the casing of the
actuator, and heat is prevented from affecting the sensor which
detects the rotation amount of the control shaft, thereby enhance
detection accuracy. In addition, since a special cooling structure
is not required, increase in size and cost of the actuator can be
avoided.
[0020] The above-mentioned object, other objects, characteristics,
and advantages of the present invention will become apparent from a
preferred embodiment, which will be described in detail below by
reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a side view of an internal combustion engine
including a variable lift valve operating system according to an
embodiment of the present invention, in a state in which the
internal combustion engine is mounted on a vehicle.
[0022] FIG. 2 is a view seen in arrow 2 in FIG. 1.
[0023] FIG. 3 is a vertical sectional side view of an intake side
valve operating system.
[0024] FIG. 4 is an exploded perspective view of the intake side
valve operating system.
[0025] FIG. 5 is an enlarged view of an essential part of FIG.
1.
[0026] FIG. 6 is a side view of an actuator.
[0027] FIG. 7 is a vertical sectional side view of the
actuator.
[0028] FIG. 8 is a sectional view taken along line 8-8 in FIG.
8.
[0029] FIG. 9 is a sectional view taken along line 9-9 in FIG.
7.
[0030] FIG. 10 is a schematic view for explaining a construction of
a default mechanism.
[0031] FIG. 11 is a sectional view taken along line 11-11 in FIG.
5.
[0032] FIG. 12 is a diagram showing efficiency of an electric
motor, generating torque of the electric motor, and generating
torque of the actuator.
[0033] FIG. 13 is a diagram showing a change in a spring force with
respect to a lift amount change of an intake valve.
[0034] FIG. 14 is a plane view briefly showing relative positions
of the internal combustion engine and a radiator in a state in
which they are mounted on a vehicle.
[0035] FIG. 15 is a plane view corresponding to FIG. 14 of a first
modified example of the embodiment.
[0036] FIG. 16 is a plane view corresponding to FIG. 14 of a second
modified example of the embodiment.
[0037] FIG. 17 is a plane view corresponding to FIG. 14 of a third
modified example of the embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] One embodiment of the present invention is described with
reference to FIGS. 1 to 14. First in FIGS. 1 and 2, a
multiple-cylinder, for example, four-cylinder engine body 22 with
an axis C of a crankshaft 21 extending along a width direction of a
vehicle is mounted on a front part of the vehicle. Cylinders are
provided in the engine body 22, side by side in a cylinder
arranging direction 23 parallel with the axis C.
[0039] The engine body 22 includes a crankcase 24 that rotatably
supports the crankshaft 21, a cylinder block 25 connected to the
crankcase 24, a cylinder head 26 connected to the cylinder block
25, and a head cover 27 which is connected to the cylinder head 26.
A cam holder 28 is connected to the cylinder head 26 at one end of
a left side along the cylinder arranging direction 23 to construct
a part of the engine body 22, and is disposed to face the outside
between the cylinder head 26 and the head cover 27.
[0040] A transmission case 32 for accommodating a transmission is
connected to a left end of the crankcase 24 in the forward
traveling direction of the vehicle, so as to form an available
space on the left side of the engine body 22 and above the
transmission case 32.
[0041] Intake ports 33 for the respective cylinders are provided at
one side wall 26a (see FIG. 1) facing a front side of the cylinder
head 26, and an intake system 34 is connected to the intake ports
33. Exhaust ports 35 for the respective cylinders are provided at
the other side wall 26b (see FIG. 1) facing a rear side of the
cylinder head 26, and an exhaust manifold 37 covered with a heat
shield cover 36 from above is connected to the exhaust ports
35.
[0042] The intake system 34 includes an air cleaner 108, an intake
chamber 109 disposed forward of the cylinder head 26 in common for
the respective cylinders, a pipeline member 110 such as a hose
which connects together the air cleaner 108 and the intake chamber
109, and a plurality of intake pipes 111 that are separated for the
respective cylinders from the intake chamber 109 and are connected
to the cylinder head 26. A pair of support legs 112 and 112 are
provided at the intake chamber 109 to extend downward, and these
support legs 112 are supported at a bracket 113 which is mounted on
the crankcase 24 via elastic members 114.
[0043] In FIGS. 3 and 4, in the cylinder head 26, a pair of intake
valves 38 are arranged for each of the intake ports 33 to be
capable of opening and closing operation, and an intake side valve
operating system 39 that drives each of the intake valves 38 to
open and close includes an intake side camshaft 41 having an intake
side valve operating cam 40 for each cylinder, an intake side
rocker arm 42 that swings following the intake side valve operating
cam 40, and is operated and connected in common with and to a pair
of intake valves 38 for each cylinder, and a variable lift
mechanism 43 that continuously changes a valve opening lift amount
among the operating characteristics of the intake valves 38.
[0044] Upper holders 44 are fastened to the cylinder head 26 to be
disposed at opposite sides of each of the cylinders except for one
end at the left side along the cylinder arranging direction 23.
Caps 45 rotatably supporting the intake side camshaft 41 in
cooperation with each of the upper holders 44 are fastened to top
surfaces of the upper holders 44. At one end at the left side along
the cylinder arranging direction 23, the end portion of the intake
side camshaft 41 is rotatably supported between the camshaft 28 and
the head cover 27.
[0045] A valve connecting part 42a, into which tappet screws 46
abutting from above on upper ends of stems 38a in a pair of intake
valves 38 are screwed so that their advance and retreat positions
are adjustable, is provided at one end portion of the intake side
rocker arm 42. A first support part 42b and a second support part
42c which is disposed below the first support part 42b are provided
at the other end portion of the intake side rocker arm 42 to
connect to each other. The first and second support parts 42b and
42c are each formed into a substantially U shape which opens on a
side opposite from the intake valves 38.
[0046] A roller 47 in rolling contact with the intake side valve
operating cam 40 of the intake side camshaft 41 is supported on the
first support part 42b of the intake side rocker arm 42 via a first
connecting shaft 48 and a needle bearing 49. The roller 47 is
disposed to be caught in the first support part 42b having a
substantially U shape.
[0047] The variable lift mechanism 43 includes a first link arm 51
which has one end portion rotatably connected to the first support
part 42b of the intake side rocker arm 42 and the other end portion
rotatably supported at a fixed support shaft 50, a second link arm
52 which has one end portion rotatably connected to the second
support part 42c of the intake side rocker arm 42 and the other end
portion rotatably supported at a movable support shaft 53, and a
control shaft 54 which is connected to the movable support shaft 53
to be capable of angularly displacing the movable support shaft 53
around an axis that is parallel with the axis of the movable
support shaft 53.
[0048] The one end portion of the first link arm 51 is formed into
a substantially U-shape to catch the first support part 42b of the
intake side rocker arm 42 from opposite sides, and is rotatably
connected to the first support part 42b via the first connecting
shaft 48 supporting the roller 47 at the intake side rocker arm 42.
The fixed support shaft 50 rotatably supporting the other end
portion of the first link arm 51 is supported by the upper holder
44.
[0049] The one end portion of the second link arm 52 disposed below
the first link arm 51 is disposed to be caught in the second
support part 42c of the intake side rocker arm 42, and is rotatably
connected to the second support part 42c via a second connecting
shaft 55.
[0050] Both the intake valves 38 are biased in a valve closing
direction by a valve spring not shown. When both the intake valves
38 which are biased in the valve closing direction by the spring
are driven in a valve opening direction with the intake side rocker
arm 42, the roller 47 of the intake side rocker arm 42 is in
contact with the intake side valve operating cam 40 due to the
biasing force of the valve spring. However, in the valve closing
state of the intake valves 38, the biasing force of the valve
spring does not act on the intake side rocker arm 42, and the
roller 47 separates from the intake side valve operating cam 40,
leading to a possibility of reducing the control accuracy of the
valve lift amount at the time of very slightly opening the intake
valves 38. Therefore, the intake side rocker arm 42 is biased in a
direction to cause the roller 47 to abut on the intake side valve
operating cam 40 by a rocker arm biasing spring 56 which is a
member separate from the valve spring.
[0051] The control shaft 54 is a single piece in common use for a
plurality of cylinders arranged in a line, and is constructed into
an integral crank shape, having webs 54a which are disposed at
opposite sides of the intake side rocker arm 42, shaft parts 54b
which perpendicularly connect to outer surfaces of base end
portions of both the webs 54a, and connecting parts 54c which
connect both the webs 54a for each cylinder. The movable support
shaft 53 having the axis parallel with the fixed support shaft 50
and the shaft parts 54b is connected to the control shaft 54 to
connect together both the webs 54a. The shaft parts 54b are
rotatably supported by the upper holders 44 and lower holders 57
which are fastened to lower surfaces of the respective upper
holders 44.
[0052] When the intake valves 38 are in the valve closing state,
the second connecting shaft 55 for connecting the second link arm
52 to the intake side rocker arm 42 is on the same axis as that of
the shaft parts 54b of the control shaft 54. When the control shaft
54 swings around the axis of the shaft parts 54b, the movable
support shaft 53 moves on an arc with the axis of the shaft parts
54b as a center.
[0053] When the control shaft 54 rotates in the direction in which
the movable support shaft 53 descends, and the roller 47 is pressed
with the intake side valve operating cam 40 of the intake side
camshaft 41, a four-joint link which connects together the fixed
support shaft 50, the first connecting shaft 48, the second
connecting shaft 55 and the movable support shaft 53, deforms to
swing the intake side rocker arm 42 downward, and the tappet screws
46 press the stems 38a of the intake valves 38 to open the intake
valves 38 with low lift.
[0054] When the control shaft 54 rotates in a direction in which
the movable support shaft 53 ascends, and the roller 47 is pressed
with the intake side valve operating cam 40 of the intake side
camshaft 41, the four-joint link deforms to swing the intake side
rocker arm 42 downward, and the tappet screws 46 press the stems
38a of the intake valves 38 to open the intake valves 38 with high
lift.
[0055] The one end portion of the control shaft 54 along the
cylinder arranging direction 23, namely, a shaft part at the one
end side along the cylinder arranging direction 23 among a
plurality of shaft parts 54b of the control shaft 54 is formed to
be relatively long as a connecting shaft part 54d. The connecting
shaft part 54d protrudes to the left side of the cylinder head 26,
and into a casing 59 of an actuator 60 which is mounted to the
outer surface of the end wall of the left side of the cylinder head
26.
[0056] In FIGS. 5 to 7, the actuator 60 comprises an electric motor
62, a deceleration mechanism 63 which decelerates output power of
the electric motor 62, a transmission mechanism 64 which is
provided between the deceleration mechanism 63 and the connecting
shaft part 54d of the control shaft 54, and a main part of a
default mechanism 65 for maintaining the connecting shaft part 54d,
namely, the control shaft 54 in a predetermined rotation position
when the electric motor 62 is not energized, which are all
accommodated in the casing 59. The casing 59 is constructed by a
casing main body 61, a first cover 74 fastened to the casing main
body 61, a lid member 82, and a second cover 88.
[0057] The deceleration mechanism 63 is provided between an output
shaft 66 of the electric motor 62 forwardly and reversely rotatable
with a default position by the default mechanism 65 as a zero
position, and a drive shaft 67 parallel with an axis of the output
shaft 66. The deceleration mechanism 63 comprises a driven gear 68
fixed to the output shaft 66, and a follow gear 69 which is meshed
with the driven gear 68 and is fixed to the drive shaft 67. The
drive shaft 67 rotates in a range of one rotation or more in
accordance with the electric motor 62 rotating within an operation
range in which the lift amount of the intake valves 38 is changed
from the maximum lift amount to the minimum lift amount, for
example, to complete closing. The power transmission means 64
comprises a worm gear 70 provided at the drive shaft 67, and a worm
wheel 71 which is meshed with the worm gear 70 and is fixed to the
connecting shaft part 54d of the control shaft 54.
[0058] A motor accommodation hole 72 circular in cross-section is
provided in a lower portion of the casing main body 61 to extend in
the longitudinal direction at the time of the engine body 22 being
mounted on the vehicle, and the electric motor 62 is fitted in and
fixed to the motor accommodation hole 72. A first cover 74 is
fastened by a plurality of bolts 73 to one side wall of the casing
main body 61 which becomes a rear side wall at the time of the
engine body 22 being mounted on the vehicle. A deceleration
mechanism accommodation part 59a which is constructed by a part of
the casing main body 61 and the first cover 74 to accommodate the
deceleration mechanism 63 is formed to extend upward above the
electric motor 62 at a position rearward of the electric motor 62
at the time of being mounted on the vehicle.
[0059] The worm gear 70 is accommodated in a worm gear
accommodation hole 75 provided in the casing main body 61 parallel
with the motor accommodation hole 72 above the motor accommodation
hole 72, and is provided on an outer periphery of the drive shaft
67 whose one end portion is rotatably supported at the casing main
body 61 via a ball bearing 76 while the other end portion is
rotatably supported at the casing main body 61 via a needle bearing
77.
[0060] Referring also to FIG. 8, a worm wheel accommodation chamber
78 leading to an intermediate portion of the worm gear
accommodation hole 75 is formed in the upper portion of the casing
main body 61, and accommodates therein the worm wheel accommodation
chamber 71. Thus, the connecting shaft part 54d of the control
shaft 54 protrudes into the worm wheel accommodation chamber 78,
and the worm wheel 71 is fastened and fixed to the connecting shaft
part 54d with a bolt 80 which is screwed into a screw hole 79
coaxially provided in an end portion of the connecting shaft part
54d.
[0061] An opening 81 is provided in an upper portion of the casing
main body 61 at a side opposite from the cylinder head 26, and a
lid member 82 which blocks the opening 81 is fastened to the casing
main body 61 with a plurality of screw members 83. Thus, a
transmission mechanism accommodation part 59b, which is constructed
by a part of the casing main body 61 and the lid member 82 to
accommodates the transmission mechanism 64, is formed to be located
forward of the deceleration mechanism accommodation part 59a at the
time of being mounted on the vehicle.
[0062] A sensor 84 being a position sensor, which detects a
rotation amount of the control shaft 54, is mounted to the lid
member 82 with a plurality of screw members 85 to oppose to the
worm wheel 65. A pair of detection holes 86 and 86 in which the
sensor 84 is engaged are provided in the worm wheel 65.
[0063] A second cover 88 is fastened by a plurality of bolts 87 to
the other side wall of the casing main body 61 on a side opposite
from the deceleration mechanism accommodation part 59a with respect
to the transmission mechanism accommodation part 59b. A default
mechanism accommodation part 59c, which is constructed by a part of
the casing main body 61 and the second cover 88 to accommodate a
main part of a default mechanism 65, is formed with the
transmission mechanism accommodation part 59b between the default
mechanism accommodation part 59c and the deceleration mechanism
accommodation part 59a.
[0064] Referring also to FIG. 9, the default mechanism 65 includes
a default shaft 96 which is a separate member from the drive shaft
67 and has an axis parallel with the drive shaft 67, a large
diameter gear 92 which is moved with and connected to the drive
shaft 67 to be rotatable around the axis of the default shaft 66, a
spring holder 93 capable of rotating around the same axis with the
large diameter gear 92, a return spring 94 (see FIG. 4) which
biases the large diameter gear 92 in a direction to abut on and
engage with the spring holder 93, and a default spring 95 which
biases the spring holder 93 in the direction opposite from the
return spring 94 in the abutting and engaging state of the large
diameter gear 92 and the spring holder 93.
[0065] The large diameter gear 92 is rotatably supported by the
default shaft 96 whose opposite ends are supported by the casing
main body 61 and the second cover 88, and is meshed with a small
diameter gear 97 provided at the other end portion of the drive
shaft 67. Namely, the large diameter gear 92 is moved with and
connected to the electric motor 62 via the small-diameter gear 97,
the drive shaft 67 and the deceleration mechanism 63, so that the
large diameter gear 92 rotates in the rotation range of less than
one rotation in accordance with the electric motor 62 rotating
within the operation range in which the lift amount of the intake
valves 38 is changed from the maximum lift amount to the minimum
lift amount, for example, to complete closing. Namely, the large
diameter gear 92 is moved with and connected to the electric motor
62 to rotate in the rotation range of less than one rotation in
accordance with the rotation of the electric motor 62 within the
range of the change in the lift amount of the intake valves 38.
[0066] The spring holder 93 is supported on the default shaft 96 to
be rotatable relatively to the large diameter gear 92. A groove 98
in the shape of an arc with the axis of the default shaft 96 as the
center is provided on the opposing surface of the large diameter
gear 92 to the spring holder 93. An engaging protrusion 99 which is
inserted in the groove 98 is provided to protrude at the spring
holder 93. Thus, the engaging protrusion 99 abuts on and engages
with one end of the groove 98 along the circumferential direction
of the large diameter gear 92 in accordance with the rotation of
the large diameter gear 92 while the lift amount of the intake
valves 38 is changed between a predetermined lift amount and the
minimum lift amount. When the large diameter gear 92 rotates to
change the lift amount of the intake valves 38 between the
predetermined lift amount and the minimum lift amount, the spring
holder 93 rotates around the same axis with the large diameter gear
92. A restricting protrusion 100 projectingly provided on the
spring holder 93 abuts on a stopper 101 (see FIG. 10) provided at
the second cover 88 in accordance with the rotation of the spring
holder 93 when the lift amount of the intake valves 38 is changed
from the minimum lift amount to the predetermined lift amount,
thereby restricting the rotation of the spring holder 93. The
rotation range of the spring holder 93 is restricted to a range
between the predetermined lift amount and the minimum lift
amount.
[0067] One end of the spiral default spring 95 is engaged with the
spring holder 93, and the other end is engaged with a pin 88a which
is implanted in the second cover 88. Thus, the default spring 95
exerts a spring force which biases the spring holder 93 from the
minimum lift amount side to the predetermined lift amount side, and
its spring load is set to be larger than the return spring 94.
[0068] Referring carefully to FIG. 4, a cylindrical spring holder
102 surrounding the connecting shaft part 54d is fixed to the
connecting shaft part 54d of the control shaft 54 inside the
cylinder head 26, and the return spring 94 that is a torsion coil
spring is wound around the spring holder 102. One end of the return
spring 94 is engaged with the cylinder head 26, and the other end
is engaged with the spring holder 102.
[0069] Namely, the return spring 94 is interposed between the
connecting shaft part 54d of the control shaft 54 and the cylinder
head 26 so as to perform not only the function of biasing the large
diameter gear 92 in the direction to abut on and engage with the
spring holder 93, but also the function of absorbing backlash
between the worm wheel 71 and the worm gear 70.
[0070] In this manner, the default mechanism accommodation part 59c
of the actuator 60 accommodates the main part except for the return
spring 94, namely, the large diameter gear 92, the spring holder 93
and the default spring 95, among the large diameter gear 92, the
spring holder 93, the return spring 94 and the default spring 95
which construct the default mechanism 65, that is, only the return
spring 94 is disposed in the cylinder head 26. A grease 103 is
charged into the default mechanism accommodation part 59c.
[0071] Describing the operation of the default mechanism 65 by
referring to FIG. 10 schematically showing the construction of the
default mechanism 65, the large diameter gear 92 is biased by the
return spring 94 from the maximum lift position to the minimum lift
position side, and the spring holder 93, which has the rotation
range restricted to the range from the minimum lift position to the
default position that is the position to provide the predetermined
lift amount of the intake valves 38, is biased from the minimum
lift position to the default position side by the default spring 95
which has a larger spring load than the return spring 94.
Accordingly, in the non-energized state of the electric motor 62,
the large diameter gear 92 is biased by the return spring 94 to
rotate to the position where the engaging protrusion 99 of the
spring holder 93 is caused to abut on and engage with one end of
the engaging groove 98; and the spring holder 93 is rotated to the
default position by the default spring 95. The large diameter gear
92, which is moved with and connected to the control shaft 54 via
the small diameter gear 94, the drive shaft 67, the worm gear shaft
70, and the worm wheel 71, also enters the default position,
whereby the lift amount of the intake valves 38 is kept at the
predetermined amount.
[0072] Incidentally, at least one of the worm wheel 71 and the worm
gear 70, which construct a part of the actuator 60 and are meshed
with each other, is formed of a synthetic resin. In this
embodiment, the worm wheel 71 is formed of a synthetic resin such
as, for example, nylon and PEEK (trade name of Victrex plc.).
[0073] As clearly shown in FIG. 8, a cylindrical barrel part 61a
leading to the worm wheel accommodation chamber 78 is provided at
the casing main body 61 of the casing 59; a cylindrical barrel part
26c which coaxially surrounds the connecting shaft part 54d of the
control shaft 54 is provided at a left end wall of the cylinder
head 26 to be fittable to the barrel part 61a; and an O-ring 104
which elastically contacts an inner periphery of the barrel part
61a is fitted to an outer periphery of the barrel part 26c. Namely,
the casing main body 61 and the cylinder head 26 are fitted to each
other in the direction along the axis of the connecting shaft part
54d of the control shaft 54.
[0074] The casing 59 of the actuator 60 is mounted astride to the
cylinder head 26 and the cam holder 28, which are the components of
the engine body constructing a part of the engine body 22.
Specifically, the casing main body 61 of the casing 59 is mounted
to the cylinder head 26 with a plurality of bolts 105 (see FIG. 5),
and also mounted to the cam holder 28 with bolts 106 (see FIG.
5).
[0075] Mounting bosses 117 having insertion holes 116 are provided
at the casing main body 61 of the casing 59 at four spots around
the electric motor 62 which is fitted in and fixed to the motor
accommodation hole 68. The casing main body 61 is fastened to the
cylinder head 26 by the bolts 105 which are inserted through the
insertion holes 116.
[0076] Ribs 118 to 125 extending to the respective mounting bosses
107 are projectingly provided on the casing main body 61. The ribs
118 and 119 are formed to cross into an X shape to connect the
upper mounting bosses 117 and the lower mounting bosses 117. The
rib 120 is formed to connect the lower mounting bosses 117. The rib
121 is formed to connect the mounting bosses 117 disposed at an
upper position and a lower position as shown in the left side part
of FIG. 5. The ribs 122 and 123 are formed to extend to the upper
mounting bosses 117, and further extend diagonally upward as
extensions of the ribs 118 and 119. The ribs 124 and 125 are formed
to diagonally intersect the ribs 122 and 123 to extend diagonally
upward from the upper mounting bosses 117 and 117.
[0077] The casing main body 61 is mounted to the cam holder 28 of
the engine body 22 at a portion corresponding to at least one of
the deceleration mechanism 63, the transmission mechanism 64 and
the default mechanism 65. In this embodiment, the casing main body
61 is fastened to the cam holder 28 with the bolt 106 at a portion
corresponding to the default mechanism 65.
[0078] In FIG. 11, a mounting boss 127 having an insertion hole 126
is provided in the casing main body 61 at the portion corresponding
to the default mechanism 65, and the bolt 106 penetrates through a
slide bush 128 which is inserted in the insertion hole 126 and is
threadedly fitted in the cam holder 28. Namely, at the portion
corresponding to the default mechanism 65, the casing main body 61
is fastened to the cam holder 28 via the slide bush 128.
[0079] The actuator 60 which controls the lift amount of the intake
valves 38 basically operates with the accelerator operation by the
vehicle driver, and when the accelerator operation is frequently
repeated in a short time, for example, during circuit traveling or
traveling on a winding road, the electric motor 62 of the actuator
60 operates in response to such a frequent operation. Thus, the
effective current passing through the electric motor 62 becomes
large, leading to a possibility that the electric motor 62
generates heat. In this case, if the heat generation of the
electric motor 62 is left as it is, there is a possibility that the
life of the electric motor 62 is reduced or a thermal distortion
generates in the casing 59 of the actuator 60. Further, there is a
possibility that the heat affects the sensor which detects the
rotation amount of the control shaft 54 to cause a detection error.
Then, if the structure for cooling the electric motor 62 is added
to the actuator 60, increase in size and cost of the actuator 60 is
provided.
[0080] Thus, the reduction ratio of the deceleration mechanism 63
is set so that efficiency of the electric motor 62 becomes the
highest when the electric motor 62 is caused to make the quickest
response in response to the frequently repeated accelerator
operation.
[0081] In this case, the efficiency of the electric motor 62 in the
actuator 60, the generation torque of the electric motor 62, and
the generation torque of the actuator 60 respectively change as
shown in FIG. 12 in accordance with the change in the rotational
speed of the electric motor 62. When the required driving torque
is, for example, 10 Nm, and the quickest response is performed in
order to overcome the required driving torque, the generation
torque of the actuator 60 is set so that the rotational speed of
the electric motor 62 becomes its highest efficiency, for example,
6200 rpm. Thus, the generation torque of the actuator 60 is
obtained by the calculation (the generation torque of the electric
motor 62.times. reduction ratio of the deceleration mechanism 63).
For example, when the rotational frequency of the electric motor 62
is set at 200 rpm, the reduction ratio of the deceleration
mechanism 63 is set at 69.3.
[0082] Next, the operation of the first embodiment is described.
The actuator 60 rotatably drives the control shaft 54 of the
variable lift mechanism 43 capable of changing the lift amount of
the intake valves 38. The actuator 60 has the drive shaft 67 moved
with and connected to the control shat 54 via the transmission
mechanism 64, and the electric motor 62 which exerts the power for
rotatably driving the drive shaft 67 to rotate it by one rotation
or more within the range of the lift amount change of the engine
valves 38. Also, the actuator 60 is provided with at least the main
part of the default mechanism 65 capable of rotatably biasing the
control shaft 54 to the position where the lift amount of the
intake valves 38 becomes the predetermined amount when the electric
motor 62 is not energized. The default mechanism 65 includes the
default shaft 96 which is the separate member from the drive shaft
67 and has the axis parallel with the drive shaft 67, the large
diameter gear 92 which is capable of rotating around the axis of
the default shaft 96 and is moved with and connected to the drive
shaft 67, and the default spring 95 which rotatably biases the
large diameter gear 92.
[0083] Therefore, the large diameter gear 92, which rotates around
the axis of the default shaft 96, can be moved with and connect to
the drive shaft 67 to rotate in the rotation range of less than one
rotation in accordance with the rotation of the electric motor 62
within the range of the lift amount change of the intake valves 38,
and thus a conventionally-used default mechanism with high
durability and reliability can be adopted.
[0084] Since the default spring 95 is a spiral type, the default
mechanism 65 can be made compact in the direction along the axis of
the default shaft 96.
[0085] As shown in FIG. 13, the default mechanism 65 keeps the lift
amount of the intake valve 38 at, for example, 1.8 mm at the time
of its operation, the gradient of the spring constant of the spiral
default spring 95 is relatively small as shown by the solid line in
FIG. 13, and therefore the load acting on the electric motor 62 is
relatively small. On the other hand, in the case where the default
spring 95 is of a coil type, the gradient of the spring constant is
relatively large as shown by the chain line in FIG. 13. Therefore,
unnecessary force is exerted on the electric motor 62 and the work
load of the electric motor 62 increases.
[0086] When the default spring 95 is of a spiral type, the sliding
friction force tends to be large due to interference between sites
adjacent in the radial direction of the default spring 95. However,
the default mechanism accommodation part 59c accommodating the main
part which includes the default spring 95 of the default mechanism
65 is formed in the casing 59 of the actuator 60, and the grease
103 is charged in the default mechanism accommodation part 59c.
Therefore, the sliding friction force is reduced, and the power
which should be exerted by the electric motor 62 is reduced to
achieve energy saving, leading to reduced fuel consumption.
[0087] When the vibration occurs due to the operation of the
electric motor 62 of the actuator 60, the vibration affects the
control accuracy of the control shaft 54, and as a result, the
exhaust property is also influenced thereby. Thus, when mounting
the actuator 60 on the engine body 22, it is necessary to firmly
fix the peripheral part of the electric motor 62 of the actuator 60
to the engine body 22 thereby enhancing vibration resistance and
durability. The casing 59 of the actuator 60 is mounted to the
engine body 22 at a plurality of spots of the portion corresponding
to the electric motor 62, and is mounted to the engine body 22 at
the portion corresponding to at least one of the deceleration
mechanism 63, the transmission mechanism 64 and the default
mechanism 65 (in this embodiment, the portion corresponding to the
default mechanism 65). That is, the portion corresponding to the
electric motor 62 which is the vibration generating source of the
actuator 60 is firmly fixed to the engine body 22, and the portion
which is relatively heavy other than the electric motor 62 is
firmly fixed to the engine body 22, thereby suppressing the
vibration. Accordingly, vibration resistance and durability of the
actuator 60 which is mounted to the engine body 22 are enhanced,
and control accuracy of the control shaft 54 and controllability of
exhaust property can be enhanced.
[0088] In the casing 59, the mounting bosses 117, though which the
bolts 105 for fastening the casing 59 to the cylinder head 26 of
the engine body 22 are inserted, are projectingly provided at the
four spots around the electric motor 62, and a plurality of ribs
118 to 125 extending to the mounting bosses 117 are projectingly
provided. Therefore, the ribs 118 to 125 prevent a distortion in
the casing 59, and an increase in the sliding friction force
between components, which are supported by the casing 59 and in
contact with each other, among a plurality of components
constructing the actuator 60, whereby the driving force which
should be exerted by the electric motor 62 is reduced to achieve
energy saving.
[0089] Moreover, the portion, which corresponds to the electric
motor 62, of the casing 59 is mounted to the cylinder head 26
constructing a part of the engine body 22, and the portion, which
corresponds to the default mechanism 65, of the casing 59 is
fastened to the cam holder 28 which constructs a part of the engine
body 22 and is connected to the cylinder head 26, via a slide bush
128. Therefore, even if there is a displacement of the mounting
surfaces of the cylinder head 26 and the cam holder 28 connected to
each other, the mounting surfaces facing the actuator 60, the
casing 59 can be assembled without distortion to the cylinder head
26 and the cam holder 28, thereby preventing increase in sliding
friction force between components, which are supported by the
casing 59 and in contact with each other, among the components
constructing the actuator 60, reducing the driving force which
should be exhibited by the electric motor 62 to achieve energy
saving, and further enhancing the control accuracy of the control
shaft 54 and controllability of exhaust property.
[0090] The reduction ratio of the deceleration mechanism 63 of the
actuator 60 is set at a value at which the maximum efficiency of
the electric motor 62 can be obtained when the quickest response is
made for required driving torque.
[0091] With such setting, when the variable lift mechanism 43 is
under the harshest operational conditions in which the electric
motor 62 operates in response to the accelerator operation being
frequently repeated in a short time during circuit traveling or
traveling on a winding road, the heat generation amount of the
electric motor 62 is minimized. Therefore, by suppressing heat
generation of the electric motor 62, the life of the electric motor
62 is extended, a thermal distortion is prevented from generating
in the casing 59 of the actuator 60, and the heat is prevented from
affecting the sensor 84 which detects the rotation amount of the
control shaft 54, thereby enhancing the detection accuracy. In this
embodiment, the worm wheel 71 constructing a part of the
deceleration mechanism 63 of the actuator 60 is formed from a
synthetic resin, thereby preventing the heat from affecting the
worm wheel 71 to enhance the durability. In addition, since a
special cooling structure is not required, increase in size and
cost of the actuator 60 can be avoided.
[0092] The deceleration mechanism accommodation part 59a
accommodating the deceleration mechanism 63, and the default
mechanism accommodation part 59c accommodating the default
mechanism 65 are formed in the casing 59 of the actuator 60 to
sandwich therebetween the worm wheel 71 and the sensor 84 which are
thermally vulnerable parts directly connected to the control shaft
54.
[0093] Accordingly, as shown in FIG. 14, even if the
rearward-blowing wind from the radiator 131 shown by the arrow 132
is blown from the front to the actuator 60 mounted to one end wall
of the engine body 22, and the rear portion of the actuator 60 is
exposed to radiation heat from the exhaust manifold 37 shown by the
arrow 133 in a state in which the engine body 22 is mounted on the
vehicle in the lateral direction behind the radiator 131, the
deceleration mechanism accommodation part 59a and the default
mechanism accommodation part 59c perform a heat shield function for
the worm wheel 71 and the sensor 84, because the worm wheel 71 and
the sensor 84 are sandwiched between the deceleration mechanism
accommodation part 59a and the default mechanism accommodation part
59 which are formed in the casing 59. Therefore, heat damage is
prevented from spreading to the worm wheel 71 and the sensor 84,
thereby enhancing durability of the worm wheel 71 and the sensor
84.
[0094] Although the sensor 84 for detecting the rotation amount of
the control shaft 54 particularly changes in characteristics in
accordance with the ambient temperature, the sensor 84 is prevented
from being directly exposed to hot air and radiation heat, thereby
enhancing detection accuracy of the sensor 84.
[0095] The synthetic resin worm wheel 71 which constructs a part of
the transmission mechanism 64 and is fixed to the control shaft 54
can reduce the weight of the actuator 60 and friction, and prevent
heat damage from spreading to the worm wheel 71. Therefore, the
reliability and durability is enhanced, and increase in friction
due to thermal deformation or the like is prevented, thereby
achieving energy saving.
[0096] As described above, the heat damage is prevented from
generating in the worm wheel 71 and the sensor 84, thereby
enhancing the degree of freedom of the mounting position of the
actuator 60. For example, as shown in a first modified example of
this embodiment shown in FIG. 15, when the engine body 22 is
mounted on the vehicle in the lateral direction behind the radiator
131, even if the side portion of the actuator 60 is exposed to
radiation heat from the exhaust manifold 37 shown by the arrow 134,
the deceleration mechanism accommodation part 59a can perform the
heat shield function for the worm wheel 71 and the sensor 84.
[0097] FIG. 16 shows a second modified example of this embodiment,
in which an engine body 22' constructed into a V shape having a
pair of banks BA and BB is mounted on the vehicle in the lateral
direction behind the radiator 131. In a state in which the
actuators 60 and 60 are mounted to one ends of both the banks BA
and BB, rearward-blowing wind of the radiator 131 and the radiation
heat of an exhaust manifold 37A are blown from the front to the
actuators 60 and 60 as shown by the arrow 135, while the rear
portions of the actuators 60 and 60 are exposed to the radiation
heat from an exhaust manifold 37B shown by the arrow 136. However,
the deceleration mechanism accommodation parts 59a and the default
mechanism accommodation parts 59c of casings 59 perform the heat
shield function for the actuators 60 and 60 as described above.
[0098] As shown in a third modified example of the present
embodiment shown in FIG. 17, when the actuators 60 and 60 are
mounted to the rear ends of both the banks BA and BB in a state in
which the engine body 22' constructed into the V shape is mounted
on the vehicle in the longitudinal direction behind the radiator
131, the side portions of the actuators 60 and 60 are exposed to
the radiation heat from the exhaust manifold 37A and the exhaust
manifold 37B as shown by the arrows 137 and 138. However, the
deceleration mechanism accommodation parts 59a and the default
mechanism accommodation parts 59c of the casings 59 perform the
same heat shield function as described above.
[0099] The embodiment of the present invention has been described,
but the present invention is not limited to the above-described
embodiment, and various changes in design can be made without
departing from the present invention described in the claims.
[0100] For example, the present invention can be carried out also
for an exhaust valve which is an engine valve.
* * * * *